1. Field of the Invention
The invention relates to telephone switching offices which utilize 1ESS or 1AESS (a trademark of AT&T Technologies, Inc.) switching equipment. In particular, the invention relates to a method and apparatus for providing the 1ESS and 1AESS switching equipment with the capability of controlling the connection, management and disconnection of telephone circuits using Signaling System #7 (SS7), a national and international standard set of protocols for providing such circuit control, and providing and receiving information via the SS7 protocol for enabling enhanced services in the switching equipment.
Further, the invention relates to apparatus interposed between the switching matrix and the customer dial pulse receivers of switching equipment such as the 1ESS switch or the 1AESS switch to collect called number digits dialed by a subscriber and change such digits as needed for enhanced services to the subscriber.
2. Description of the Prior Art
The existing telephone network in the United States of America is largely a remnant of the earlier AT & T Network which was divested into several regional holding companies pursuant to an order of a Federal Court. This existing network had been designed to provide the equivalent of an electrical connection between two points in the network. The only information originating within the telephone network, and the conveyance of this information, was related to the provision of a basic capability to connect the two points.
Advances in the state of the art of communications have lead to the possibility of providing the existing services of the telephone network in a more efficient manner while simultaneously establishing the foundation for new network services beyond the capability of the existing network. The realization of this possibility has resulted in both national and international development of new standards for communication protocols between the switching elements within the telephone network. These new standards are widely referred to as "Signaling System #7 (SS7)". For example, see TR-NPL-000246 "Bell Communications Research Specification of Signaling System No. 7, Revision #2, June 1987."
Providing SS7 capability to a No. 5 crossbar switch or the 1ESS and 1AESS switching systems has heretofore been accomplished by the apparatus and method described in U.S. Pat. No. 4,853,955, issued Aug. 1, 1989 and entitled "APPARATUS AND METHOD FOR PROVIDING EXISTING TELEPHONE SWITCHING EQUIPMENT WITH THE CAPABILITY OF USING THE SS7 PROTOCOL".
Other than the apparatus and method described in U.S. Pat. No. 4,853,955, the provision of SS7 capability within 1ESS and 1AESS switching systems would require an expensive upgrade or the replacement of the switch with a newer version. The difficulty of accomplishing the conversion of such switches is demonstrated by the inability of the trunk circuit interfaces on these switches to support the out-of-band signaling method employed by SS7 and by the lack of the capability for processing the SS7 protocol messages used to implement the services.
As the majority of telephones in the United States of America are connected to 1ESS (a Trademark of AT&T Technologies, Inc.) or 1AESS (a Trademark of AT&T Technologies, Inc.) switches, the replacement or upgrading of these switches would require vast economic expenditures by the telephone companies. Estimates of this replacement cost for a typical central office are frequently in excess of $3 million. The incurring of such costs for the replacement of switching equipment which is functioning well is not justified by initial increases in revenues from the provision of more efficient switching.
The present invention provides a method and apparatus for implementing SS7 capabilities within 1ESS and 1AESS Class 5 central offices. This is accomplished without affecting the underlying operating principles of the existing switching office. In addition, the SS7 capability is provided in a cost effective manner without adversely affecting the quality of service as perceived by the subscribers connected to such a switching office. Further, the SS7 capability is provided in such a manner so as not to adversely affect the operation of the upgraded switching office or the rest of the telephone system.
The SS7 protocol requires that the control signals for the management of the telephone circuits be transmitted from the calling switching office to the receiving switching office on a separate circuit from the trunk circuit on which the telephone message information is transmitted.
The present invention provides a switch command monitor interconnected to the switching processor to monitor the status of subscriber lines and connections to service circuits such as customer dial pulse receivers, ring generators and trunk circuits used for incoming or outgoing calls. The switch command monitor provides these functions and others which relate to determining switch connections between the lines, trunks and service circuits and provides this information to an adjunct processor. The present invention also includes a receiver module interposed between the existing switching matrix and the existing customer dial pulse receiver for examining the dialed digits to identify the specific call and the type of trunk circuit required (i.e. SS7, non-SS7 or intra-office), and the type of service required.
The receiver module thus collects the dialed digits and changes these digits as needed for enhanced services and provides the changed digits to the customer dial pulse receiver. In performing these functions the receiver module also provides, or is transparent to, all the functions provided by the customer dial pulse receiver. A trunk circuit interface is also coupled to the existing switching system for generating a trunk circuit identification signal which is related to the specific call. A processing unit is coupled to the switch command monitor, the receiver module, and the trunk circuit interface of receiving the signals representing the calling number, the called number, and the trunk circuit identification, all of which are related to the specific call. These signals are then transmitted on a separate line to the receiving switching office for management of the switching circuits on the receiving end to couple the incoming call to the correct receiving subscriber on the correct trunk circuit.